U.S. patent number 7,870,723 [Application Number 11/354,768] was granted by the patent office on 2011-01-18 for system and method to operate fuel cell in the exhaust of an internal combustion engine.
This patent grant is currently assigned to Ford Global Technologies, LLC. Invention is credited to David Bidner, Shane Elwart, James Kerns, Gopichandra Surnilla.
United States Patent |
7,870,723 |
Elwart , et al. |
January 18, 2011 |
System and method to operate fuel cell in the exhaust of an
internal combustion engine
Abstract
A method for operating an international combustion engine, the
engine also includes a first cylinder, a second cylinder, an
exhaust system, and a fuel cell in the exhaust system. The method
comprises operating the first cylinder lean to provide air to the
fuel cell during at least one condition; and operating the second
cylinder rich or stoichiometric to provide torque output and fuel
to the fuel cell.
Inventors: |
Elwart; Shane (Ypsilanti,
MI), Kerns; James (Trenton, MI), Surnilla;
Gopichandra (West Bloomfield, MI), Bidner; David
(Livonia, MI) |
Assignee: |
Ford Global Technologies, LLC
(Dearborn, MI)
|
Family
ID: |
38366884 |
Appl.
No.: |
11/354,768 |
Filed: |
February 14, 2006 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20070186537 A1 |
Aug 16, 2007 |
|
Current U.S.
Class: |
60/286; 60/275;
60/285; 60/274 |
Current CPC
Class: |
F01N
3/10 (20130101); F01N 13/009 (20140601) |
Current International
Class: |
F01N
3/00 (20060101) |
Field of
Search: |
;60/274,275,285,299,286,295,301 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Denion; Thomas E
Assistant Examiner: Tran; Diem
Attorney, Agent or Firm: Lippa; Allan J. Alleman Hall McCoy
Russell & Tuttle LLP
Claims
The invention claimed is:
1. A method for operating an international combustion engine, the
engine also including a first cylinder, a second cylinder, an
exhaust system, a fuel cell in the exhaust system, the method
comprising: during at least one condition, operating the first
cylinder lean to provide air to the fuel cell; operating the second
cylinder rich or stoichiometric to provide torque output and fuel
to the fuel cell; and adjusting a richness of fuel injection to the
second cylinder to adjust a power output of the fuel cell, the
adjustment being based on a temperature of the fuel cell.
2. The method of claim 1, wherein the operating the first cylinder
lean includes passing air to the cylinders without fuel
injection.
3. The method of claim 1, wherein the method further comprises
operating the first cylinder to provide an engine torque output
until the fuel cell is warm, and then passing air to the cylinders
without fuel injection.
4. The method of claim 2, wherein the first cylinder is different
from the second cylinder on one of displacement and cylinder
structure.
5. The method of claim 1, wherein the method further comprises
adjusting a leanness of fuel injection to the first cylinder to
adjust the power output of the fuel cell.
6. The method of claim 1, wherein the engine torque output is
compensated using adjustment of one of throttle opening, spark
timing, and valve timing.
7. The method of claim 1, wherein the air to the fuel cell is
supplied solely by the first cylinder of the engine.
8. The method of claim 1, wherein the air the fuel cell is supplied
by the engine and an air pump separate from an engine air supply
system.
9. The method to claim 1, wherein the fuel cell is one of solid
oxide fuel cell, Molten Carbonate fuel cell, and proton exchange
membrane fuel cell.
10. A method for operating an international combustion engine, the
engine also including a first cylinder, a second cylinder, a fuel
injector, an exhaust manifold, an exhaust system and a fuel cell
downstream of the exhaust manifold, the method comprising: during
at least one condition operating the first cylinder lean to provide
air to the fuel cell; operating the second cylinder rich to provide
an engine torque output and supply fuel to the fuel cell; and
injecting fuel into the exhaust system to reform the fuel.
11. The method of claim 10, wherein the operating the first
cylinder lean includes passing air to the cylinders without fuel
injection.
12. The method of claim 10, wherein the air to the fuel cell is
supplied solely by the first cylinder of the engine.
13. The method of claim 10, wherein the method further comprises
adjusting the richness of fuel injection to the second cylinder to
adjust the power output of the fuel cell.
14. The method of claim 10, wherein the method further comprises
injecting fuel into the exhaust manifold of the engine.
15. The method of claim 10, wherein the engine is a direct
injection engine wherein the fuel is injected during the exhaust
stroke of the second cylinder.
16. An internal combustion engine of a vehicle comprising: a first
cylinder; a second cylinder; an exhaust system; a fuel cell in the
exhaust system; a fuel injector coupled to an exhaust manifold to
supply fuel to the fuel cell, the exhaust manifold being insulated
to be used as a thermal reactor for fuel reformation; and a
controller to operate the first cylinder lean during at least one
condition and the second cylinder rich or stoichiometric.
17. The system of claim 16, wherein the first cylinder is inducted
with air without fuel during the operation.
18. The system of claim 16, wherein the first cylinder is different
from the second cylinder on one of displacement and structure.
19. A vehicle system, comprising: a direct fuel injection engine
with a first and a second cylinder; an exhaust system; a fuel cell
in the exhaust system; and a controller to operate the first
cylinder lean during at least one condition and the second cylinder
rich or stoichiometric, wherein during the at least one condition
fuel is injected during an exhaust stroke to provide reformed fuel
to the fuel cell.
Description
FIELD
The present application relates to a system and method to operate a
fuel cell in the exhaust of an internal combustion engine, and more
specifically to a system and method to run the engine to provide
air and fuel to the fuel cell in the exhaust.
BACKGROUND
Internal combustion engines use only a portion (for example,
approximately 31% to 38% in some cases) of the supplied fuel energy
due to heat wasted, friction, incomplete combustion, and others. In
addition, approximately 3-17% of the supplied fuel energy can be
used to maintain the engine operation during standby and another
1-2% can be used to operate accessories. Therefore, it can be
advantageous to utilize the waste energy, typically in the form of
thermal and chemical energy, to improve the overall vehicle system
fuel efficiency.
One approach to utilize the waste energy is to arrange a solid
oxide fuel cell (SOFC) in an exhaust system of an internal
combustion engine. Specifically, the U.S. patent application Ser.
No. 2004/0177607 describes an internal combustion engine with a
SOFC in an exhaust system. The SOFC is of a structure that fuel can
be reformed inside the fuel cell. In the '607 reference, one
embodiment includes a fuel adding injector disposed between the
engine and the SOFC (see FIG. 8). The fuel added to the exhaust
passage can be used as power generation fuel for the SOFC. The
embodiment also includes a heat exchanger and an air pump. The air
with its temperature raised in the heat exchanger is introduced
into the exhaust passage at the upstream side of SOFC so as to
raise the wall surface temperature of the exhaust passage and the
exhaust gas. Thus, evaporation of the fuel added from the fuel
adding injector can be advanced.
However, the inventors herein have recognized several disadvantages
of such an approach. For example, additional devices such fuel
pump, fuel adding injector, air pump, and heat exchanger are
required for the operation of the SOFC. These separate air and fuel
supply systems plus the heat exchanger can be expensive or may
become degraded over time. Further, the system may only use fuel
cells that can perform fuel reformulation. Furthermore, the
reformation of fuel in the SOFC may cause emissions such as NOx
emissions.
SUMMARY
The above disadvantages are overcome by a method for operating an
international combustion engine, the engine also including a first
cylinder, a second cylinder, an exhaust system, and a fuel cell in
the exhaust system. The method comprises during at least one
condition, operating the first cylinder lean to provide air to the
fuel cell; and operating the second cylinder rich or stoichiometric
to provide torque output and fuel to the fuel cell.
In this way, some engine cylinders can be used as an air pump to
supply desired oxygen to the fuel cell. Thus, in one embodiment, it
may be possible to eliminate an air pump to the fuel cell, thus
reducing system cost. In some embodiments, the operation of
cylinder may provide air if the air pump to the fuel cell becomes
degraded or supplement air if the air pump cannot supply enough
air. Further, in some embodiments, since some cylinders of engine
operate rich, they may supply the required fuel to the fuel cell,
thus saving cost for a separate fuel supply system and
reformer.
According to another aspect, a method for operating an
international combustion engine is provided. The engine also
includes a first cylinder, a second cylinder, a fuel injector, an
exhaust manifold, an exhaust system and a fuel cell downstream of
the exhaust manifold. The method comprises during at least one
condition operating the first cylinder lean to provide air to the
fuel cell; operating the second cylinder rich to provide an engine
torque output and supply fuel to the fuel cell; and injecting fuel
into the exhaust system.
Again, such a method can provide various advantages. For example,
fuel injection may provide additional fuel when the engine is
unable to provide sufficient fuel to the fuel cell. Further, with a
direct injection engine, since fuel can be injected during the
exhaust stroke, a separate fuel injector may not be needed. Thus,
the cost for additional fuel supply system to the fuel cell may be
saved.
According to yet another aspect, an internal combustion engine of a
vehicle comprises a first cylinder; a second cylinder; an exhaust
system; a fuel cell in the exhaust system; and a controller to
operate the first cylinder lean during at least one condition and
the second cylinder rich or stoichiometric.
BRIEF DESCRIPTION OF DRAWINGS
FIG. 1 is a schematic diagram of an engine in an example hybrid
powertrain.
FIG. 2 is a schematic diagram of one embodiment of an internal
combustion engine.
FIG. 3 is a schematic diagram of one embodiment of an exemplary
system wherein the fuel cell is disposed in the exhaust of an
engine.
FIG. 4 is a flow diagram of one embodiment of a method of operating
an engine to supply air and fuel to a fuel cell.
FIG. 5 is a flow diagram of one embodiment of a method of an engine
operation to increase the temperature of an exhaust entering a fuel
cell.
FIG. 6 is a schematic diagram of one embodiment of an engine system
with fuel cell and catalyst.
FIG. 7 is a schematic diagram of another embodiment of an engine
system with fuel cell and catalysts.
FIG. 8 is a schematic diagram of an exemplary embodiment of a
catalytic device comprising a fuel cell portion and a catalytic
conversion portion.
FIG. 9 is a schematic view of an exemplary embodiment of a
catalytic device comprising a fuel cell portion and a catalytic
conversion portion, illustrating a first exemplary oxidant
inlet.
FIG. 10 is a schematic view of an exemplary embodiment of a
catalytic device comprising a fuel cell portion and a catalytic
conversion portion, illustrating a second exemplary oxidant
inlet.
FIG. 11 is a flow diagram of one embodiment of a method to control
the emissions by adjusting air/fuel ratio of an engine.
FIG. 12 is a flow diagram of one embodiment of a method of using a
fuel cell as air/fuel ratio sensor.
FIG. 13 is a flow diagram of one embodiment of a method to diagnose
the functioning of a fuel cell and/or an air fuel ratio sensor.
FIG. 14 is a schematic diagram of one embodiment of an exemplary
system wherein the exhaust speciation is determined.
DETAILED DESCRIPTION
The system and method of the present application may be used in
hybrid electric vehicles (HEVs). FIG. 1 demonstrates just one
possible configuration, specifically a parallel/series hybrid
electric vehicle (split) configuration. However, other hybrid
configurations may be used, such as series, parallel, integrated
starter-alternator, or others.
In an HEV, the engine 24 is coupled to the planet carrier 22 of
planetary gear set 20. A one way clutch 26 allows forward rotation
and prevents backward rotation of the engine and planet carrier.
The planetary gear set 20 also mechanically couples a sun gear 28
to a generator motor 30 and a ring (output) gear 32. The generator
motor 30 also mechanically links to a generator brake 34 and is
electrically linked to a battery 36. A traction motor 38 is
mechanically coupled to the ring gear 32 of the planetary gear set
20 via a second gear set 40 and is electrically linked to the
battery 36. The ring gear 32 of the planetary gear set 20 and the
traction motor 38 are mechanically coupled to drive wheels 42 via
an output shaft 44.
Fuel cell 25 is disposed in the exhaust system of engine 24. In
addition, fuel cell 25 is electrically linked to battery 36.
The planetary gear set 20, splits the engine 24 output energy into
a series path from the engine 24 to the generator motor 30 and a
parallel path from the engine 24 to the drive wheels 42. Engine 24
speed can be controlled by varying the split to the series path
while maintaining the mechanical connection through the parallel
path. The traction motor 38 augments the engine 24 power to the
drive wheels 42 on the parallel path through the second gear set
40. The traction motor 38 also provides the opportunity to use
energy directly from the series path, essentially running off power
created by the generator motor 30. This reduces losses associated
with converting energy into and out of chemical energy in the
battery 36 and allows all engine 24 energy, minus conversion
losses, to reach the drive wheels 42.
Thus, FIG. 1 shows that in this example, the engine 24 is attached
directly to planet carrier 22, for example without a clutch that
can disconnect them from each other. One way clutch 26 allows the
shaft to rotate freely in a forward direction, but grounds the
shaft to the powertrain's stationary structure when a torque
attempts to rotate the shaft backwards. Brake 34 does not interrupt
the connection between the sun gear 28 and the generator motor 30,
but can, when energized, ground the shaft between those two
components to the powertrain's stationary structure.
A vehicle system controller (VSC) 46 controls many components in
this HEV configuration by connecting to each component's
controller. An engine control unit (ECU) 48 connects to the Engine
24 via a hardwire interface (see further details in FIG. 2). In one
example, the ECU 48 and VSC 46 can be placed in the same unit, but
are actually separate controllers. Alternatively, they may be the
same controller, or placed in separate units. The VSC 46
communicates with the ECU 48, as well as a battery control unit
(BCU) 45 and a transaxle management unit (TMU) 49 through a
communication network such as a controller area network (CAN) 33.
The BCU 45 connects to the battery 36 via a hardwire interface. The
TMU 49 controls the generator motor 30 and the traction motor 38
via a hardwire interface. The control units 46, 48, 45 and 49, and
controller area network 33 can include one or more microprocessors,
computers, or central processing units; one or more computer
readable storage devices; one or more memory management units; and
one or more input/output devices for communicating with various
sensors, actuators and control circuits.
It should be appreciated that the system and method of the present
application may be used in any other HEV configurations. Additional
details and examples of engine 24 and fuel cell 25, as well as
other components, are described in more detail below herein, such
as in FIGS. 2-3.
FIG. 2 is a schematic diagram of one embodiment of an internal
combustion engine 24. Engine 24 may be a gasoline engine or a
diesel engine, for example. Thus, the example of FIG. 2 shows a
gasoline engine with a spark plug, however, engine 24 may be a
diesel engine without a spark plug, or any other type of engine.
Internal combustion engine 24, comprising a plurality of cylinders,
one cylinder of which is shown in FIG. 2, is controlled by
electronic engine controller 48. Engine 24 includes combustion
chamber 29 and cylinder walls 31 with piston 35 positioned therein
and connected to crankshaft 39. Combustion chamber 29 is shown
communicating with intake manifold 43 and exhaust manifold 47 via
respective intake valve 52 and exhaust valve 54. While only one
intake and exhaust valve is shown, more than one may be used if
desired. For example, two intake valves and a single exhaust may be
used, or two intake and two exhaust valves may be used.
In this example, variable valve timing may be provided by variable
cam timing. While in this example independent intake cam timing and
exhaust cam timing is shown, variable intake cam timing may be used
with fixed exhaust cam timing, or vice versa. Also, various types
of variable valve timing may be used, such as the hydraulic
vane-type actuators 53 and 55 receiving respective cam timing
control signals VCTE and VCTI from controller 48. Cam timing
(exhaust and intake) position feedback can be provided via
comparison of the crank signal PIP and signals from respective cam
sensors 50 and 51.
In an alternative embodiment, cam actuated exhaust valves may be
used with electrically actuated intake valves, if desired. In such
a case, the controller can determine whether the engine is being
stopped or pre-positioned to a condition with the exhaust valve at
least partially open, and if so, hold the intake valve(s) closed
during at least a portion of the engine stopped duration to reduce
communication between the intake and exhaust manifolds.
Intake manifold 43 is also shown having fuel injector 65 coupled
thereto for delivering liquid fuel in proportion to the pulse width
of signal FPW from controller 48. Fuel is delivered to fuel
injector 65 by fuel system (not shown) including a fuel tank, fuel
pump, and fuel rail (not shown). In addition, intake manifold 43 is
shown communicating with optional electronic throttle 125.
Distributorless ignition system 88 provides ignition spark to
combustion chamber 29 via spark plug 92 in response to controller
48.
Controller 48 is shown in FIG. 2 as a conventional microcomputer
including: microprocessor unit 102, input/output ports 104, and
read-only memory 106, random access memory 108, keep alive memory
110, and a conventional data bus. Controller 48 is shown receiving
various signals from sensors coupled to engine 24, in addition to
those signals previously discussed, including: engine coolant
temperature (ECT) from temperature sensor 112 coupled to cooling
sleeve 114; a position sensor 119 coupled to an accelerator pedal;
a measurement of engine manifold pressure (MAP) from pressure
sensor 122 coupled to intake manifold 43; a measurement (ACT) of
engine air charge temperature or manifold temperature from
temperature sensor 117; and an engine position sensor from a Hall
effect sensor 118 sensing crankshaft 39 position. In one aspect of
the present description, engine position sensor 118 produces a
predetermined number of equally spaced pulses every revolution of
the crankshaft from which engine speed (RPM) can be determined.
In an alternative embodiment, a direct injection type engine can be
used where injector 65 is positioned in combustion chamber 29,
either in the cylinder head similar to spark plug 92, or on the
side of the combustion chamber.
FIG. 3 shows one embodiment of an exemplary engine system where the
fuel cell 225 is disposed in the exhaust of the engine 224. Engine
224 may be an engine described in FIG. 2 and other internal
combustion engines. Engine 224 and fuel cell 225 may be used in the
exemplary HEV as described in FIG. 1 or in other HEV
embodiments.
During engine operation, where the engine 224 combusts fuel and
produces torque output, fuel energy unutilized for torque output
may be discharged in the form of unburnt fuel, reformed fuel such
as hydrogen and carbon monoxide (CO), and heat. In addition, oxygen
may be contained in the exhaust depending on the air-fuel ratio,
such as whether the engine operates lean or rich. In some examples,
the richness of the engine air-fuel ratio may be adjusted to vary
the amount of unburned and/or reformed fuel provided to fuel cell
225 based on conditions of the fuel cell, such as temperature,
efficiency, etc. Further, in other embodiments, the engine may be
adjusted to concurrently supply both fuel and oxygen to the fuel
cell, such as by operating some cylinders lean and other cylinders
rich.
As shown in FIG. 3, fuel cell 225 is disposed in the exhaust and
downstream of engine 224. Fuel cell 225 may utilize fuel, air, and
heat discharged from engine 224 to generate electrical power. Fuel
cell 225 may be a solid oxide fuel cell (SOFC), molten carbonate
fuel cell, proton exchange membrane (PEM) fuel cell, etc.
Some types of fuel cells may operate at temperatures higher than a
room temperature. For example, the operating temperature for a SOFC
may range approximately from 700 to 1,000.degree. F. Fuels used in
the reaction in the fuel cell may be reformed fuel such as hydrogen
(H.sub.2) and carbon monoxide (CO), among others. For example, in
the case of a SOFC, at the anode or the fuel electrode, H.sub.2 or
CO reacts with oxygen ions transferred in the electrolyte to form
H.sub.2O or CO.sub.2 and releases four electrons. At the cathode or
air electrode, the oxygen in the air obtains four electrons and
becomes an oxygen ion. The oxygen ion moves toward the anode. Thus,
current or electrical power is generated from the chemical
reactions. The products of the fuel cell 225 may be H.sub.2O,
CO.sub.2, oxygen, NOx generated from engine 224 as well as fuel
such as CO and H.sub.2 passing through the fuel cell 225 without
reaction. In addition, exhaust heat may be released from fuel cell
225.
The current generated from fuel cell 225 may be stored in a
battery, such as battery 236, or directly used to power electrical
accessories of the vehicle, or directly provided to a motor to
assist in engine rotation or in driving the vehicle's wheels.
In some embodiments, battery 236 may supply current to fuel cell
224 to determine the speciation of gas stream entering and exiting
fuel cell 225 as described in detail herein. In one embodiment,
fuel cell 225 and battery 236 are controlled by controller 248,
which also controls engine operation as described in conjunction
with FIG. 2. In another embodiment, fuel cell 225 and battery 236
may share a common controller. In yet another embodiment, each of
fuel cell 225 and battery 236 may have an individual
controller.
Engine 224 may be operated in a way that the fuel energy exhausted
during engine operation can be sufficiently used by the downstream
fuel cell 225. Alternatively, engine 224 may be operated to
maintain an operation of the downstream fuel cell to generate a
desired electrical power.
In addition to generate electric power, the fuel cell may provide
information about the exhaust. For example, the speciation at each
fuel cell may be determined by correlation between the modeled
engine outputs of species in conjunction with modeled temperature
at each fuel cell. Inclusion of an electrode across the catalytic
diffusion layer and the fuel cell will provide a way to
periodically apply a pumping current across a cell. FIG. 14 is a
schematic diagram of one embodiment of an exemplary system wherein
the exhaust speciation may be determined. The relationship of the
applied pumping current at a cell or a variety of cells
corresponding to the pumping voltage may change with the air/fuel
ratio or related to the air/fuel ratio as shown at 1412. Therefore,
in some embodiments, the pumping current/voltage relationship may
be used to directly derive the air/fuel ratio at a given cell.
Further, by using engine operating parameters such as engine speed
(N), load, air mass (AM) or air flow, cam timing, spark timing,
engine coolant temperature (ECT), etc., exhaust temperature may be
inferred from a model as shown at 1414. Furthermore, the feed
exhaust speciation of a cell may be inferred from a model based on
engine parameters such as engine speed, load, air mass or air flow,
cam timing, spark timing, engine coolant temperature, etc. as shown
at 1416. Based on information from 1414, fuel cell temperature at
each cell may be inferred from a model at 1420. With the cell
air/fuel ratio, inferred cell temperature, inferred feed
speciation, a cell space velocity, and a model of the
reduction/oxidation methods of the catalytic cell, the fuel cell
speciation at each cell may be inferred as shown at 1430. Thus, the
exhaust speciation or exhaust information may be obtained.
In some embodiments, this approach of determining the speciation
may be used to further reduce certain emissions such as NOx
emissions at each cell by applying a current across the catalytic
layer, the cell and/or reversing the potential across the cell as
described in more details below.
Referring now to FIG. 4, it illustrates an exemplary embodiment of
a control method to operate an engine to supply air and fuel to a
fuel cell, where some cylinders operate at a different air-fuel
ratio than other cylinders during engine operation. For example,
some cylinders can operate rich while other cylinders concurrently
operate lean, thereby providing both air and fuel to the fuel cell.
Further, it may be possible in some cases to adjust the respective
lean and rich air-fuel ratios of the cylinders to supply a desired
level of fuel cell power generation. However, under other
conditions, the level and/or number of lean and/or rich cylinders
may be varied with conditions of the fuel cell, such as generated
power or current, to reduce emissions while still generating
power.
Specifically, the method 400 includes, at 402, operating selected
cylinders lean to supply air to a fuel cell downstream of an
exhaust system of an engine. When the selected cylinders operate
lean, the exhaust may contain oxygen, thus providing oxygen for the
reaction in the fuel cell.
In some embodiments, the selected cylinders may be a group of
cylinders in one bank of the engine. In one embodiment, the
selected cylinders are operated in an injector cutout mode without
fuel injection. Alternatively, the selected cylinders may be used
to supply power to the vehicle by combusting fuel following a cold
start. Then, after the fuel cell is warm and active, these
cylinders may be operated in a fuel cut mode to supply air to the
fuel cell. Further, the number of cylinders operated lean or
without injected fuel may be varied based on exhaust temperature,
conditions of the fuel cell, desired engine output, or others.
Thus, in some embodiments, selected engine cylinders may be used as
an air pump to supply air to the fuel cell. In one embodiment, the
selected cylinders may have different configuration from the
primary cylinders in the engine. For example, the cylinders may
have different displacement or piston structure. In another
example, the cylinders may not be equipped with a fuel supply,
ignition source, and/or variable valve timing.
Next, the method 400 includes, at 404, operating selected cylinders
rich to supply fuel to the fuel cell. In some embodiments, the
selected cylinders may be in one bank of the engine. Alternatively,
the cylinders may be randomly selected to operate rich, where the
number or sequencing of such cylinders can vary with operating
conditions such as temperature, fuel cell conditions, or
others.
Next, the method 400 includes, at 406, injecting fuel to the
exhaust system to reform and supply fuel to the fuel cell, if
desired. Under some operating conditions, the engine is unable to
provide sufficient hydrogen and carbon monoxide for the fuel cell.
The method 400 approaches this situation by injecting fuel into the
exhaust system to reform and supply fuel. In some embodiments, fuel
may be injected into the exhaust manifold along with some amount of
air. In one embodiment, this air may be diverted from the fuel cell
air supply such as an air pump. In another embodiment, this air may
be supplied by running the engine leaner. Such injected fuel may be
reformed into hydrogen and/or carbon monoxide suitable for
reactions in the fuel cell using heat from the exhaust manifold,
for example.
In some embodiments, steam or water vapor may be mixed with fuel
and air in the exhaust system to enhance the fuel reformulation. In
one embodiment, the engine exhaust manifold may be configured to
have a large volume and be insulated to maintain high temperature.
In this way, the exhaust manifold may be served as a thermal
reactor for fuel reformation. Alternatively, with a direct
injection engine, fuel may be injected into selected cylinders
during the exhaust stroke. In some embodiments, the selected
cylinders may be in one bank of the engine, and the number of
cylinders operated with late injection during the exhaust stroke,
and/or the amount of late injection, may be varied with fuel cell
operating conditions, such as generated power or current, and
exhaust conditions, such as temperature. Alternatively, the
cylinders may be randomly selected to perform fuel injection during
the exhaust stroke, or varied in a preselected pattern. The high
temperature after a power stroke may favor the reformation of fuel
in the cylinder, under some conditions, thus providing improved
performance with late injection. Further, fuel reformation may
continue in the exhaust manifold to increase the amount of reformed
fuel.
The above method has various advantages. For example, some engine
cylinders can be used as an air pump to supply desired oxygen to
the fuel cell. Thus, in one embodiment, it may be possible to
eliminate, or supplement, an air pump in providing oxygen to the
fuel cell, thus reducing system cost. In some embodiments, the
operation of cylinders at a lean or injector cut-out condition may
provide additional air to the exhaust and fuel cell in the event
the air pump degrades. Further, under conditions where the air pump
may supply insufficient oxygen, the above operation may also be
used to supplement air.
Further, in some embodiments, since some cylinders of engine
operate rich, they may supply the required fuel to the fuel cell.
Additionally, fuel injection to the exhaust system may provide
additional fuel when the engine is unable to provide sufficient
fuel to the fuel cell, for example. Further, with a direct
injection engine, since fuel can be injected during the exhaust
stroke, a separate fuel injector may not be needed. Thus, in some
embodiments, the cost for a separate fuel supply system and
reformer may be avoided or reduced via late injection supplementing
separate exhaust injection.
Referring now to FIG. 5, it shows a flow diagram of one embodiment
of a method of engine operation to increase the temperature of an
exhaust entering a fuel cell. Specifically, the method 500
includes, at 502, determining the fuel cell temperature. Next, the
method compares the temperature with a threshold at 504. The
threshold may be at or above a minimum temperature at which the
fuel cell is able to function at a specified performance level. If
the temperature is determined to be greater than the threshold at
504, then no action is required. If the temperature is determined
to be less than the desired value at 504, then the method includes,
at 506, adjusting engine operating conditions to increase the heat
flow in the exhaust. In some embodiments, the heat output of the
engine may be increased by operating the engine with a more
retarded spark timing in conjunction with a larger air/fuel flow
(to maintain torque). Alternatively, the engine may be operated
rich and air may be injected into the exhaust stream. In one
embodiment, the injected air may be air diverted from the pump used
to supply the fuel cell. In another embodiment, some cylinders can
operate rich and some cylinders can operate lean. In this way, the
combustion products from the rich operation of the engine may react
with air in an exothermal reaction to release heat and increase
temperature.
As described above, the temperature of a fuel cell may be
maintained in a selected range for desired operation. When the
engine serves as a heat source for a fuel cell, it can take time to
heat the fuel cell to the desired operating temperature under some
conditions such as cold start, or deceleration fuel shut off. By
performing the routine 500, the fuel cell temperature may be raised
quickly to a temperature range desired for the desired operation of
the fuel cell.
Referring to FIG. 6, it shows a schematic diagram of one embodiment
of an engine system with fuel cell and catalyst. As shown in FIG.
6, NOx reducing catalyst 620 is disposed in the engine exhaust
passage 612 downstream of engine 624 and upstream of the fuel cell
625. Exhaust exiting NOx reducing catalyst enters fuel cell 625
through passage 622. Fuel cell 625 is electrically communicated
with battery 636.
An air/fuel ratio sensor 652 is shown to be placed before fuel cell
625 and an air/fuel ratio sensor 654 is shown to be placed after
fuel cell 625. Sensors 652 and 654 may be HEGO sensor, Universal
Exhaust Gas Oxygen (UEGO), or other air/fuel ratio sensors.
Alternatively, a two-state exhaust gas oxygen sensor may be
substituted for sensors 652 and 654.
Fuel cell temperature may be measured by temperature sensor 656,
and/or estimated based on operating conditions such as engine
speed, load, air temperature, engine temperature, and/or airflow,
or combinations thereof.
Engine controller 648 receives signals from sensors in addition to
signals described above in conjunction with FIG. 2.
In the embodiment illustrated in FIG. 6, fuel may be added to the
engine exhaust by fuel supply system 640. Alternatively, fuel may
be added to the exhaust manifold or may be injected into a cylinder
during the exhaust stroke if the engine is a direct injection
engine. In some embodiments, the engine may operate in a rich mode
and may provide all fuel required for the operation of fuel cell
625.
Similarly, air required for fuel cell 625 may be supplied by air
pump 660. Alternatively, the engine may be operated in a way to
supply the required air. For example, as described above, the air
pump may be selected cylinders or a designated cylinder of engine
624, where the cylinder may operated in a fuel cut state. In some
embodiments, air may be supplied by engine having selected
cylinders running lean.
The engine may operate rich during power cogeneration with the fuel
cell. In the rich operating mode, there can be relatively low
emissions of NOx. In the illustrated embodiment, NOx reducing
catalyst 620 is disposed downstream of engine exhaust and upstream
of fuel cell 625. NOx reducing catalyst may be a NOx catalyst or a
lean NOx trap. On the NOx reducing catalyst, NOx can be reduced to
N.sub.2 and O.sub.2 while unburnt fuel, reformed fuel, CO, H.sub.2,
etc. pass through to enter fuel cell 625.
In the fuel cell, CO, H.sub.2, and HC are oxidized into CO.sub.2
and H.sub.2O. Therefore, through proper control of its operating
conditions, the fuel cell may reduce CO, H.sub.2, and HC emissions
to a desirable level. Specifically, the oxidation reactions in the
fuel cell may be controlled by adjusting air/fuel ratio of engine
based on sensor 650 and/or sensor 652, as well as conditions of the
fuel cell and other operating conditions. Various example control
strategies are described in more detail below.
In some embodiments, a platinum group metal (PGM) may be
incorporated into fuel cell 625 to enhance the oxidation efficiency
of fuel cell. PGM may be platinum, palladium, or other precious
metals. In such a configuration, CO, H.sub.2, and HC may be
oxidized in the reactions on the surface of PGM in addition to the
reactions at the electrodes of the fuel cell.
The system described above may have various advantages. For
example, NOx emissions are reduced in the NOx reducing catalyst
specifically designed for NOx removal. Thus, the catalyst may be
optimized to enhance the NOx removal efficiency. Further, when the
engine operates rich, the NOx reducing catalyst is in the oxygen
deficient environment. Thus, the NOx reduction reaction can be
favored. Furthermore, since the NOx reduction reaction can be an
exothermic reaction, having a NOx reducing catalyst upstream of
fuel cell can be advantageous for the operation of fuel cell. For
example, the heat released from the exothermic reaction may raise
the temperature of the fuel cell to a level that gives improved
fuel cell operation. Additionally, since the temperature in NOx
reducing catalyst 620 and exhaust passage 622 is higher, more fuel
may be reformed when unburnt fuel from the engine and/or fuel
supply system pass through NOx reducing catalyst 620 and exhaust
passage 622.
It should be appreciated that an emissions control device to
control NOx may be eliminated in some embodiment if NOx emissions
resulting from rich operation can meet the emission standard, or if
other approaches may be used to meet regulated emission levels.
Additionally, the fuel cell may serve as an emission control device
to decrease CO, H.sub.2, HC emissions by oxidizing them into
CO.sub.2, H.sub.2O while generating power. Thus, it may be possible
to eliminate oxidizing catalysts or three way catalyst
converters.
FIG. 7 is a schematic diagram of another embodiment of emission
reduction system. The system comprises engine 724, NOx reducing
catalyst 720 downstream of engine 724, fuel cell 725 downstream of
NOx reducing catalyst 720, and oxidizing catalyst 760. NOx reducing
catalyst 720 communicates with engine 724 via exhaust passage 712.
Fuel cell 725 communicates with NOx reducing catalyst 720 through
exhaust passage 722 and communicates with the oxidizing catalyst
via exhaust passage 732. The system further comprises fuel supply
system 740 supplying fuel to fuel cell 725, and air pump 760
supplying air to fuel cell 725 and oxidizing catalyst 760. Fuel
cell 725 electrically communicates with battery 736. Optionally,
sensors 750 and 752 are placed before and after fuel cell 725, and
sensor 754 is placed after oxidizing catalyst. The sensors send
exhaust information to controller 748 which controls operations of
the system.
The embodiment depicted in FIG. 7 is similar to the embodiment
depicted in FIG. 6, however, the embodiment of FIG. 7 includes the
addition of oxidizing catalyst 760 downstream of fuel cell 725 and
the supply of air to oxidizing catalyst 760. Oxidizing catalyst 760
can be beneficial in that it may further reduce CO, H.sub.2, HC
emissions passing through fuel cell 725 unreacted. Alternatively, a
three way catalyst converter (TWC) may be used in place of
oxidizing catalyst 760 to reduce emissions of NOx, CO, H.sub.2, HC,
etc. In such a configuration, a sensor such as oxygen sensor may be
placed in the TWC. Thus, exhaust information in the TWC may be sent
to controller in time for the adjustment of engine operation.
FIG. 8 shows an internal structure of an exemplary embodiment of a
catalytic device. The internal structure may be a combination of a
fuel cell and a catalyst. The catalytic device includes an internal
structure having a fuel cell portion and a catalytic conversion
portion. FIG. 8 shows a schematic diagram of an exemplary
embodiment of an internal structure 810 of a catalytic device.
Internal structure 810 has a fuel cell portion and a catalytic
conversion portion. Internal structure 810 includes a support 812,
an anode 814 supported by a first surface of support 812, a cathode
816 supported by a second surface of support 812, and a catalytic
conversion structure 818 supported by the first surface of support
812. FIG. 8 shows anode 814 and cathode 816 disposed on opposite
sides of support 812, and catalytic conversion structure 818
disposed on anode 814. However, it will be appreciated that other
intermediate layers between these layers may be used. Furthermore,
it will be understood that catalytic conversion structure 818 may
be disposed over only portions of anode 814, or may substantially
cover anode 814. Likewise, anode 814 and cathode 816 may each
completely cover the respective support surfaces, or only partially
cover the support surfaces. Additionally, while the term "internal
structure" is used to describe the structure forming and/or
supporting the fuel cell and catalytic conversion structures, it
will be appreciated that at least portions of the internal
structure 810 may be exposed to the atmosphere outside of the
catalytic device, as described in more detail below.
Support 812, anode 814, and cathode 816 cooperate to form a fuel
cell structure 820 for generating an electrical potential from
unoxidized and/or partially oxidized exhaust components supplied to
anode 814, in combination with oxygen (or other oxygen-containing
oxidant) supplied to cathode 816. Examples of exhaust components
that may be used as fuel by fuel cell structure 820 include, but
are not limited to, hydrogen, carbon monoxide, and unoxidized and
partially oxidized hydrocarbons.
Catalytic conversion structure 818 may be configured to be porous
or otherwise permeable by exhaust gases so that such exhaust gases
may reach those portions of anode 814 covered by catalytic
conversion structure 818 for consumption by fuel cell structure
820. Furthermore, catalytic conversion structure 818 may help to
reform hydrocarbons in the exhaust, thereby forming more fuel for
fuel cell structure 820. Catalytic conversion structure 818
additionally may oxidize any hydrogen, carbon monoxide,
hydrocarbons, and other oxidizable exhaust components not consumed
by fuel cell structure 820, and also may be configured to reduce
NO.sub.x, emissions. In this manner, catalytic conversion structure
818 and fuel cell structure 820 may cooperate to generate an
electrical potential from exhaust gases and to reduce the
concentration of undesirable emissions in the exhaust from engine
24.
The use of the catalytic device with the internal structure
described in FIG. 8 may offer various advantages over the use of
separate oxidative catalytic devices and fuel cells in an emissions
system. For example, in applications where a catalytic converter is
separated from a fuel cell along an exhaust system, heat produced
by the catalytic reactions within the catalytic conversion device
may be lost. In contrast, the configuration of fuel cell structure
820 and catalytic conversion structure 818 may allow heat produced
by catalytic conversion structure 818 to be used to heat fuel cell
structure 820. This may be helpful, as the thermal energy that
would otherwise be wasted in a conventional catalytic converter
system may be used to heat fuel cell structure 820 to its ordinary
operating temperatures, which may be on the order of 800-1000
degrees Celsius for some types of fuel cell such as SOFC.
Furthermore, the use of catalytic device may help to reduce the
number of components used in an emissions system relative to the
use of a separate catalytic converter and fuel cell.
Engine 24 may be operated in such a manner that the engine produces
alternating periods of rich and lean exhaust. Such an oscillation
of the air/fuel ratio is often used, for example, with three-way
catalysts for ordinary catalyst operation. In the context of
catalytic device with internal structure 810, periods of rich
exhaust may be used to supply fuel to fuel cell structure 820, and
periods of lean exhaust may be used to increase the oxygen content
of catalytic conversion structure 818 to facilitate the catalytic
oxidation of exhaust components. In some embodiments, the
oscillation of the air/fuel ratio may be conducted substantially
symmetrically about the stoichiometric point, while in other
embodiments the air/fuel ratio may be oscillated about a midpoint
offset from the stoichiometric point, either to the rich side or
lean side of stoichiometry. Oscillating the air/fuel ratio about a
midpoint richer than the stoichiometric point may provide more fuel
in the form of unoxidized and partially oxidized exhaust products
to fuel cell structure 820 relative to oscillating the air/fuel
ratio about the stoichiometric point or a leaner ratio.
In some embodiments, a rectifier 822 may be used to smooth the
output of fuel cell structure 820. Rectifier 822 may be used, for
example, in embodiments in which an oscillating or otherwise
variable air/fuel ratio is used to operate engine 24, as the
oscillation of the air/fuel ratio may produce an uneven fuel cell
output. Any suitable rectification circuit or circuits may be used
as rectifier 822. Suitable circuits include circuits configured to
output a suitable voltage and/or current for a desired application.
For example, rectifier 822 may include one or more diodes or like
circuit elements to help prevent reversal of current flow in the
event of variations in exhaust composition.
Any suitable material may be used as support 812. For example, in
some embodiments, support 812 may be made at least partially of a
solid electrolyte material capable of conducting oxygen ions
between cathode 816 and anode 814. In other embodiments, support
812 may be made from a material that is not ionically conductive,
but that is coated with an ionic conductor such that an ionically
conductive path exists between cathode 816 and anode 814. In yet
other embodiments, support 812 may be formed from more than one
ionically conductive material. Examples of suitable ionically
conductive materials for support 812 may include, but are not
limited to, zirconium oxide-based materials. Support 812 may have a
honeycomb-like structure typically used in the construction of
three-way catalytic converters, or may have any other suitable
structure.
Likewise, anode 814 and cathode 816 may be formed from any suitable
material or materials. Suitable materials for use as anode 814 and
cathode 816 include materials having similar thermal expansion
characteristics as support 812, as internal structure 810 of a
catalytic device may undergo thermal cycling from very cold
temperatures (for example, while engine 24 is at rest in a cold
climate) to the very hot temperatures often used to operate solid
oxide fuel cells. As a prophetic example, it may be possible to use
materials similar in design to EGO, UEGO, NOx sensors, where the
thermal expansion rates of the materials are selected so as to
reduce or eliminate the transfer of species from the anode and
cathode layer. This is because, for example, these type of sensors
are generally configured to be capable of operation under the same
environmental conditions as a solid oxide fuel cell.
Catalytic conversion structure 818 also may be formed from any
suitable material or materials. Suitable materials include, but are
not limited to, conventional three-way catalytic wash coats. Such
wash coats may include, but are not limited to, barium and cerium
as well as platinum group metals including, but not limited to
platinum, palladium and rhodium.
Catalytic device with internal structure 810 may include a
structure for preventing oxidant and fuel from reaching the
incorrect electrodes. For example, support 812 may have a
honeycomb-like interior configuration, and a continuous outer
surface formed at least partially from an ionically conductive
material (or coated with an ionically conductive material)
surrounding the honeycomb material, thereby containing exhaust
gases within the honeycomb material. In these embodiments, anode
814 may be deposited over internal surfaces of support 812, and
cathode 816 may be deposited over the outside face of the
continuous outer surface of support 812. Exhaust from engine 24 may
be directed into the internal portions of support 812, and the
continuous outer surface of the support may prevent the exhaust
from reaching cathode 816.
Catalytic device with internal structure 810 may be configured to
provide oxidant to cathode 816 in any suitable manner. For example,
the catalytic device may be configured to provide air to cathode
816. FIG. 9 shows a schematic depiction of a structure for
providing ambient air to cathode 816, and for preventing air from
reaching anode 814. Catalytic device 900 includes an outer casing
920 substantially enclosing internal structure 810. Outer casing
920 includes one or more openings 902 configured to allow air to
reach cathode 816 disposed on the outer surface of support 812.
Furthermore, a seal 904 may be provided between an upstream end of
internal structure 810 and outer casing 920, thereby preventing
exhaust gases from reaching cathode 816. An additional seal 906 may
be provided between a downstream end of internal structure 810 and
outer casing 920, thereby offering further protection against
oxygen from reaching the anode and exhaust gases from reaching the
cathode.
In some embodiments, a catalytic device with internal structure 810
may be configured to receive oxidant gases from a source other than
ambient air. For example, in some embodiments, catalytic device may
be configured to receive oxidant gases for use by cathode 816 from
one or more engine cylinders that are configured to produce lean
exhaust. In these embodiments, different cylinders in engine 24 may
be configured to operate simultaneously at different air/fuel
ratios.
FIG. 10 shows, generally at 1000, a schematic depiction of an
embodiment of a catalytic device configured to receive oxidant
gases from one or more engine cylinders. Catalytic device 1000 is
configured to receive exhaust from a first exhaust conduit 1002 for
providing a first input to a first electrode, and exhaust from a
second exhaust conduit 1004 for providing a second input to a
second electrode. An internal structure 1006 includes a fuel cell
structure and a catalytic conversion structure, as described above
in the context of the embodiment of FIG. 8. The first electrode
(not shown) is formed on or adjacent to (or is otherwise supported
by) an interior surface 1008 of internal structure 1006, and the
second electrode (not shown) is formed on or adjacent to (or is
otherwise supported by) an outer surface 1010 of internal structure
1006.
In some embodiments, the first input from first exhaust conduit
1002 may be exhaust from rich-burning cylinders and the second
input from second exhaust conduit 1004 may be exhaust from
lean-burning cylinders. In these embodiments, the first electrode
may be an anode and the second electrode may be a cathode.
In other embodiments, the first input from first exhaust conduit
1002 may be exhaust from lean-burning cylinders and the second
input from second exhaust conduit 1004 may be exhaust from
rich-burning cylinders. In these embodiments, the first electrode
may be a cathode and the second electrode may be an anode. In
either case, a seal 1212 may be provided between an upstream end of
internal structure 1006 and an outer casing 1014 to prevent exhaust
gases from first exhaust conduit 1002 from reaching the second
electrode adjacent to outer surface 1010 of structure 1006, and to
prevent exhaust gases from second exhaust conduit 1004 from
reaching the first electrode adjacent to interior surface 1008.
Furthermore, casing 1014 may be configured to contain exhaust gases
such that exhaust gases that flow into catalytic device 1000
through second exhaust conduit 1004 and that are not consumed by
the fuel cell structure flow out of casing 1014 through second
exhaust conduit 1004. Additional catalytic devices may be disposed
in second exhaust conduit 1004 and/or first exhaust conduit where
desired. It will be appreciated that a catalytic conversion
structure (for example, a three-way catalyst wash coat) may be
disposed partially or fully over either of the first electrode on
interior surface 1008 of internal structure 1006, and/or over the
second electrode on the exterior surface 1010 of internal structure
1006.
It should be appreciated that an engine having catalytic device
1000 may be operated using control method 400 as illustrated in
FIG. 4 and corresponding description above. In one embodiment,
first conduit 1002 or second conduit 1004 may be connected to a
cylinder that is used as an air pump to supply air to the fuel
cell.
In addition to advantages described above, the catalytic devices
depicted in FIGS. 8-10 may save cost and provide flexibility for
exhaust system design. For example, in one embodiment, since the
catalytic device may function as both fuel cell and catalyst, it
may replace separate fuel cells or separate catalysts such as those
illustrated in FIG. 6 or FIG. 7, for example.
FIG. 11 is one embodiment of a method or routine to control
emissions using operating conditions of the fuel cell. The method
includes, at 1104, determining a desired air/fuel ratio of exhaust
entering the fuel cell, where the air/fuel ratio can be
proportional to oxidant/reductant ratio. Thus, controlling the
air/fuel ratio enables control of the oxidant/reductant ratio, at
least under some conditions. In some embodiments, the desired
air/fuel ratio may be determined based on actual performance of the
fuel cell, such as generated current or voltage, and/or exhaust
information from sensors upstream and downstream of fuel cell, for
example. In addition, the desired air-fuel ratio may be based on a
desired level of power generation, or based on engine or vehicle
information, such as the time since an engine start, or others.
Next, the method 1100 includes, at 1106, adjusting the air/fuel
ratio of the engine based on an operating condition of the fuel
cell and the desired value. The operating condition of the fuel
cell may be based on exhaust information which may include feedback
from exhaust air-fuel ratio sensors (such as sensor upstream and
downstream of the fuel cell), as well as an indication of exhaust
air-fuel ratio from the fuel cell, as is described in more detail
below herein with regard to FIG. 12. In some embodiments, the
engine and/or exhaust air/fuel ratio may be adjusted by varying the
air/fuel ratio entering the intake manifold of the engine. In other
embodiments, the air-fuel ratio of the exhaust may be adjusted by
varying injected air and/or fuel in the exhaust. In still another
embodiment, combinations of the above adjustments may be used.
For example, in one embodiment, some cylinders may be operated rich
and some cylinders may be operated lean, where the exhaust mixture
air-fuel ratio of the cylinders may be adjusted by varying the lean
and/or rich air-fuel ratio of the individual cylinders. In another
embodiment, selected cylinder may be operated as an air pump
without fuel injection, and by changing the number of such
cylinders, the mixture air-fuel ratio may be adjusted. In still
other embodiments, fuel may be injected during an exhaust stroke if
the engine is a direct injection engine to adjust the exhaust
air-fuel ratio. Alternatively, an air or a fuel supply system
separate from the engine supply system may be used to introduce air
and fuel into the exhaust.
Next, the method 1100 includes, at 1108, determining a desired
amount of air in the exhaust entering the oxidizing catalyst, since
oxygen can be required for the oxidation reaction in the oxidizing
catalyst. The desired amount may be determined by comparing exhaust
information obtained from sensors before and after the oxidizing
catalyst, for example. Next, the method 1100 includes, at 1110,
adjusting the amount of air entering the oxidizing catalyst to the
desired value based on an operating condition of the oxidizing
catalyst. The amount of air may be adjusted by mixing air from a
fuel cell air pump with the exhaust from the fuel cell. The fuel
cell air pump may be a pump separate from engine air supply.
Alternatively, selected cylinders operating lean may provide air.
In some embodiments, the combined engine and fuel cell exhaust
streams may be mixed with air before entering the oxidizing
catalyst or in the oxidizing catalyst.
Alternatively, a TWC may be used in place of oxidizing catalyst.
The reactions in the TWC may also be controlled by adjusting the
amount of air entering the TWC.
This approach can provide various advantages, such as in the case
where the engine may be operated dependent on an operating
condition of the fuel cell. In one embodiment, the engine air-fuel
ratio may be adjusted based on information from the fuel cell
indicative of exhaust air/fuel ratio of the exhaust before, in, or
after the fuel cell. Specifically, by adjusting the air/fuel ratio
of the engine in this way, the emissions from the fuel cell may be
decreased, and/or the power generation of the fuel cell may be
increased. In other words, while the engine operates as a primary
power source, the engine may also be adjusted so that the emissions
may be sufficiently controlled in a fuel cell.
Referring to FIG. 12, it shows one embodiment of an exemplary
method or routine to control engine operation based on an air/fuel
sensor and/or information from a fuel cell indicative of air-fuel
ratio. The method 1200 includes, at 1202, determining a desired
air/fuel ratio of an engine based on an operating condition. The
operation conditions may be the operating conditions of the engine,
transmission, or catalyst. Next, the method 1200 includes, at 1204,
determining open loop fuel injection and/or air amount based on the
desired air fuel ratio and operating condition, e.g. manifold air
flow (MAF).
Next, the method 1200 includes, at 1206, determining if a feedback
adjustment is enabled based on an operating condition. If the
answer is no, the routine adjusts fuel injection and air induction
based on the open loop at 1216. If the answer is yes, the method
1200 includes, at 1208, reading one or more air/fuel ratio sensors
if there is any in the system. The air/fuel ratio sensor may be a
HEGO sensor, a UEGO sensor or other suitable sensors. Next, the
method 1200 includes, at 1210, diagnosing if the fuel cell and/or
air/fuel ratio sensor is functioning, such as whether it is
functioning to provide information regarding a measured air-fuel
ratio. If the answer is no, the routine adjusts fuel injection and
air induction based on the open loop value from 1216. If the answer
is yes, the method 1200 includes, at 1212, determining feedback
adjustment based on the air/fuel ratio sensor(s) and/or fuel cell
output(s), such as current, voltage, etc. Next, the method 1200
includes at 1214, adjusting fuel injection and/or air induction
into the engine, or into the exhaust, based on open loop and feed
back adjustments to achieve the desired air fuel ratio. Thus,
desired air/fuel ratio may be obtained through an open loop and/or
closed loop fuel injection.
Thus, the method 1200 may use the fuel cell as an air/fuel ratio
sensor, among others. In one example where the fuel cell may be
constructed similar to a Nernst cell, it can be used to determine
the air/fuel ratio as a function of the electrical output such as
current, voltage, or impedance. For example, the Nernst equation
can be used in conjunction with engine speciation and temperature
models to determine speciation at the fuel cell. Alternatively, the
supply and exhaust speciation of the fuel cell may be inferred by
supplying current to the upstream cell and observing the change in
current as a result of the previous intrusive action. Therefore,
the air/fuel ratio can be determined.
Note that when current is applied to the fuel cell, NOx at the
anode may receive electrons and be reduced to N.sub.2 and O.sub.2.
Thus, it may be possible to configure the fuel cell to reduce NOx
by supplying approximately 5.8 kJ per mole of NOx or about 0.002
hpxhr per mol of NOx to form N.sub.2 and O.sub.2. The number or
constant of 5.8 kJ per mole or 0.002 hp.times.hr per mol of NOx is
the change in gibbs energy, required to disassociate NOx at
atmospheric conditions, this may change depending on the
environmental conditions of the cell. In some embodiments, the
current may be applied across the catalytic layer and/or the fuel
cell. In other embodiments, the current may be applied by reversing
the potential across the cell.
Using a fuel cell as a sensor, in addition to a power generation
and emission reduction device, may have various advantages. First,
it may be possible to reduce a number of exhaust air/fuel ratio
sensors, thus reducing system cost. Further, the fuel cell can be
used as an additional air/fuel ratio sensor to supplement other
air/fuel ratio sensor information. Additionally, in one embodiment,
when current from a battery is applied to the fuel cell, NOx
emissions can be decreased by reducing NOx to N.sub.2 and O.sub.2.
Therefore, the fuel cell may serve multiple functions such as power
generation, sensing, and/or emission control.
Further, in another embodiment, information such as voltage or
current generation of the fuel cell may be used to adjust engine
operation other than, or in addition to, combustion or exhaust
air-fuel ratio. For example, the engine may be adjusted to vary the
speciation in the exhaust to adjust fuel cell operation in response
to measurement of fuel cell conditions.
FIG. 13 illustrates one embodiment of a method or routine to
diagnose the functioning of an air/fuel ratio sensor and/or a fuel
cell. The routine 1300 includes, at 1320, determining whether a
diagnostics based on the fuel cell is enabled. If the answer is no,
the diagnostic routine is ended. If the answer is yes, the routine
includes, at 1340, determining the conditions of the air/fuel ratio
sensors and/or fuel cell based on an electrical output of the fuel
cell. Next, the routine 1300 includes, at 1360, determining whether
the electrical output valves are outside a predetermined range. The
predetermined range may be the range that the fuel cell and
air/fuel ratio sensor are expected to be within given current
operating conditions. If the answer is no, the fuel cell and
air/fuel ratio sensor are deemed functioning, and the diagnostic
routine ends. If the answer is yes, the routine 1300 diagnose, at
1380, that fuel cell and/or air fuel sensor is degraded.
Thus, in one example, the routine uses a condition of the fuel cell
to diagnose the functionality of an air-fuel ratio sensor. In
another example, the routine may use a condition of the air-fuel
ratio sensor to determine the functionality of the fuel cell. The
routine thus allows the fuel cell to have a diagnostic function in
addition to power generation.
As will be appreciated by one of ordinary skill in the art, the
specific routines and block diagrams described below in the
flowcharts may represent one or more of any number of processing
strategies such as event-driven, interrupt-driven, multi-tasking,
multi-threading, and the like. As such, various steps or functions
illustrated may be performed in the sequence illustrated, in
parallel, or in some cases omitted. Likewise, the order of
processing is not necessarily required to achieve the features and
advantages of the disclosure, but is provided for ease of
illustration and description. Although not explicitly illustrated,
one of ordinary skill in the art will recognize that one or more of
the illustrated steps or functions may be repeatedly performed
depending on the particular strategy being used. Further, these
Figures graphically represent code to be programmed into the
computer readable storage medium in controller 48.
It will be appreciated that the processes disclosed herein are
exemplary in nature, and that these specific embodiments are not to
be considered in a limiting sense, because numerous variations are
possible. The subject matter of the present disclosure includes all
novel and non-obvious combinations and subcombinations of the
various camshaft and/or valve timings, fuel injection timings, and
other features, functions, and/or properties disclosed herein.
The following claims particularly point out certain combinations
and subcombinations regarded as novel and nonobvious. These claims
may refer to "an" element or "a first" element or the equivalent
thereof. Such claims should be understood to include incorporation
of one or more such elements, neither requiring nor excluding two
or more such elements. Other combinations and subcombinations of
the injection and valve timing and temperature methods, processes,
apparatuses, and/or other features, functions, elements, and/or
properties may be claimed through amendment of the present claims
or through presentation of new claims in this or a related
application. Such claims, whether broader, narrower, equal, or
different in scope to the original claims, also are regarded as
included within the subject matter of the present disclosure.
* * * * *